1. Ch. 6
The Muscular System

2. Case Study Investigation
You are selected for an internship at the National Space Biomedical Research Institute in Houston, Texas. Part of your job is to monitor the health of the astronauts for the National Aeronautics and Space Administration (NASA) before, during, and after a space mission. By chance, your time in the lab corresponds with the return of an American astronaut from the International Space Station. She just spent 171 days in the space station and is now getting back to her research studies on earth. Unfortunately, it was discovered that she would have to go through at least 3 weeks of physical therapy.

3. You learned from reading her physical health report that she lost 30% of her skeletal muscle mass. Most of it occurred within the last 2 months of the mission in space. The normal muscle loss during a space mission is less than 20%. A majority of muscle atrophy results from disuse, yet she followed all the exercise programs NASA requires. Your job is to assist the research team in investigating her problem.
By the end of this chapter, you
will be asked to determine the
most likely cause of her
accelerated loss of muscle mass.

4. Applied Learning Outcomes
Use the terminology associated with the musculature system
Learn about the following:
Different types of muscle cells
Muscle tissue development
Gross and fine muscle structure
Gross muscle function
Muscle cell physiology
Muscle types and actions
Muscle development and growth
Understand the aging and pathology of the musculature

5. Overview
Muscle cells change their shape by shortening or contracting. They are composed of specialized contractile cells.
Over half the body’s mass is composed of muscle tissue, and over 90% of this muscle tissue is involved in skeletal movement.
Muscles require glucose, oxygen, calcium and electrolytes and release metabolic wastes.
Chapter 6 – The Muscular System

6. Muscle Three types of muscle are found in the human body:
a) Cardiac muscle
(slightly striated
& involuntary;
b) Skeletal muscle
(striated &
voluntary)
c) Smooth muscle
(non-striated &
involuntary)
Smooth Muscle: Found in the linings of blood vessels and tubular organs; provide the body with weak contractions that can last for long periods of time
Cardiac Muscle: The muscle of the heart
Skeletal Muscle: Muscle attached to bone; produces body movement
Smooth and Cardiac muscle are involuntary – they work without conscious effort
Skeletal muscle is voluntary – under conscious control

7. Skeletal Muscle Function
1. Skeletal Movements = pulling on bone (relaxation / contraction)
Prime mover =muscle
responsible for the movement
Synergist = muscles that
help the prime mover
Antagonist = muscle that produces the opposite movement as prime mover

8. 2. Posture / Muscle Tone: balance weight distribution and hold muscles in position
a. tonic contraction:
only a few muscles
contract at a time;
NO shortening and
NO movement

9. Regulate Organ Volume
a. sphincters: bands of smooth muscle that prevent outflow of fluids from hollow organs

10. Move substances within the body:
a. cardiac muscle – pumps blood
smooth muscle – moves food through digestive sys. (peristalsis)

11. Heat Production: when muscles contract they produce heat
Hypothermia – decrease in
body temp below normal
b. Hyperthermia – increase in
body temp above normal

12. raises eyebrow
closes jaw
closes eyes
smile muscle
closes jaw
closes lips
yes/no muscle
extends head / neck

13. Muscles of the Trunk deltoid adducts abducts arm arm adducts upper arm
flex trunk

14. MUSCLES of the ARM flexes forearm pronates & supinates flexes elbow
extends
elbow
flexes forearm
pronates & supinates

15. Quadriceps extend the leg Vastus intermedius (inner quadricep)
flexes thigh + lower leg
(middle quadricep)
Quadriceps
extend the leg
(lateral quadricep)
(medial quadricep)
Vastus intermedius
(inner quadricep)
plantar-flexes ankles
dorsi-flexes ankles
plantar-flexes ankles

16. Hamstrings flex the leg extends thigh adducts thigh (lateral hamstring
(middle hamstring)
(medial hamistring)

17. Musculature: Gross Anatomy
1. Origin: stationary bone the muscle attaches to
(zygomatic arch)
Musculature: Gross Anatomy
2. Body: rest of the muscle
(masseter)
3. Insertion: moveable bone the muscle attaches to
(mandible)

18. Origin: Scapula / Humerus Body Biceps Brachii Insertion: Radius Tendon
Sacs of synovial fluid btwn
tendon & bone for lubrication
Body
Biceps
Brachii
Insertion:
Radius
Tendon
attachs muscle
to bone

19. What are muscles composed of that allow them to do their jobs?
Concept Check #1
What are muscles composed of that allow them to do their jobs?
specialized contractile cells
2. What are 5 functions of the muscular system.
1- movement posture regulate organ volume
4 – move substances w/I body heat production
3. How are the prime mover, synergist, and antagonist involved in movement? If I were to flex my elbow what muscles would represent the PM, S, and A?
Prime mover – main muscle responsible for movement (bicep)
Synergist – other muscles that help PM (brachioradialis)
Anatogonist – produces opposite movement (tricep)
4. What is a tonic contraction and give an example of one.
No movement and no shortening of a muscle
Ex. pulling up on something heavy

20. 5. How do sphincters regulate organ volume?
Concept Check #2
5. How do sphincters regulate organ volume?
Smooth muscle prevents fluid from flowing out of a hollow cavity
6. Give an example of how cardiac and smooth muscle move substances within the body.
Cardiac muscle – pumps blood throughout the body
Smooth muscle – moves food throughout the body (peristalsis)
7. How does the origin and insertion of a muscle differ? How are they involved in muscle movement?
Origin – immovable bone that muscle attaches to
Insertion – movable bone that muscle attaches to
The insertion bone moves towards the origin bone
8. Research the origin and insertion for the following muscles:
Gastrocnemius: Origin: femur Insertion: achilles tendon
Pectoralis major: Origin: clavicle /sternum Insertion: humerus

21. Skeletal Muscle Structure
surrounds fassicles
surrounds each
surrounds entire
muscle
bundle of muscle cells
Muscle Structure Animation

22. Microcopic Muscle Cell Structure
skeletal muscle cells are LONG, CYLINDRICAL cells covered with an excitable membrane called the sarcolemma
sarcolemma contains proteins that respond to signals from other cells/environment and transmits the information to the muscle cells causing them contract

23. chains of sarcomeres form myofibrils sarcomere contains
contractile unit of muscle is called a sarcomere (thousands run the length of a muscle cell)
chains of sarcomeres form myofibrils
sarcomere contains
2 types of myofilaments
1. thick m.f. contain
protein myosin
2. thin m.f.  contain
proteins actin,
tropomyosin
& troponin
sarcoplasmic reticulum
surrounds sarcomeres &
stores Ca for contractions
Sarcomere
marks
boundaries
between
sarcomeres

24. Sarcomere Chain Actin (thin) Myosin (thick)
Actin (thin)
Myosin (thick)

25. (basic neuromuscular junction animation)
Muscle Cell Function
contraction occurs when sarcomeres shorten simultaneously
Nerve Stimulation – takes place at the neuromuscular junction (motor neuron meets muscle fiber)
Ca causes nerve cell to release acetylcholine, a neurotransmitter, which binds to sarcolemma and allows Na+ /K to cross membrane
(basic neuromuscular junction animation)

26. Muscle Contraction – takes place inside muscle cell
ion movement causes SR releases Ca which travels to sarcomere to start contraction
Ca binds to troponin & removes tropomyosin ( blocks myosin heads from attaching to actin)
Myosin attaches & pulls on actin  shortens sarcomere  shortens muscle Sliding filament theory animation

27. Rigor Mortis  muscle tension caused by Ca leakage out of SR into sarcomere after death
Creatine phosphate, glycogen, & myoglobin  all serve as energy or oxygen reserves for muscle contraction

28. Sliding Filament Model
Muscle Relaxation: when neural stimulations stop exciting the sarcolemma
Na+/K+ levels are completely recovered; SR regains most Ca
troponin/tropomyosin covers binding site  myosin releases actin  sarcomere relaxes  muscle elongates
Sliding
Filament
Model

29. Types of Skeletal Muscle Fibers Fast White Twitch Fibers
unique muscle composition is genetically determined
Feature
Slow Red Twitch Fibers
(Type I)
Fast White Twitch Fibers
(Type IIb)
Size
Smallest
largest
Mitochondria
large amount
(get ATP through aerobic processes)
small amount
(get ATP through anaerobic processes)
Color
red
(high myoglobin content)
white
(low myoglobin content)
Speed of Contractions
Slow
Fast
Resistance to Fatigue
High (very fatigue resistant)
Low (not fatigue resistant)
Activities
Maintaining posture, endurance activities (i.e. marathon runners)
Muscle: soleus
Rapid, intense movements of short duraction (i.e. sprinters, throwing a ball or weight lifting)
Muscle: gastrocnemius / vastus lateralis

30. Concept Check #3
9. List the three membranes of muscle in order from superficial to deep then explain how they each differ.
10. What is the name given to the membrane that surrounds a muscle cell and why is it important?
What is a sarcomere? And how do the 2 myofilaments that make up a sarcomere differ?
12. Draw a picture of a sarcomere and label the two different myofilaments.

31. What is the neuromuscular junction and what occurs here?
Concept Check #4
13. Why is the sarcoplasmic reticulum that surrounds the sarcolemma so important?
14. Describe the steps that must occur for a muscle to contract and then relax.?
What is the neuromuscular junction and what occurs here?
16. Why is Ca necessary for starting a muscle contraction?

32. 17. Explain the sliding filament theory (shortening of a sarcomere).
Concept Check #5
17. Explain the sliding filament theory (shortening of a sarcomere).
19. Why would a leak of Ca from the sarcoplasmic reticulum cause rigor mortis.
When does a muscle relax?
21. Why might marathon runners have more red twitch fibers and sprinters have more white twitch fibers? Include speed of contraction and fatigue resistance in your explanation.

33. (determined by genetic differences & different blood flow patterns)
Skeletal Muscle Action
skeletal muscle structure responds to the amount of work it must do
irregular use or lack of neural stimulation
 cells lose sarcomere proteins
 contraction strength decreases
 muscle size decreases
(hypotrophy/atrophy)
regular use & increased blood flow
 muscle strength increases
 muscle size increases (hypertrophy)
Does your muscle diameter increase OR does your sarcomere density & strength increase w/o a significant increase in overall muscle size ???
(determined by genetic differences & different blood flow patterns)

34. shortening of the muscle brings the insertion closer to the origin
Skeletal Muscle Action
shortening of the muscle brings the insertion closer to the origin
threshold stimulus - minimal level of stimulus required to cause a fiber to contract
muscle cells are controlled by different motor units with different threshold levels so not all muscles contract at the same time
All or None Theory – a fiber contracts completely or not at all; It’s the difference in picking up 1 textbook or 25 textbooks.
Strength = contracting more fascicles
Endurance = producing more
contracting and relaxing groups
of fascicles.

35. muscles can be categorized by the effect it has on joint motion
Skeletal Muscle Action
muscles can be categorized by the effect it has on joint motion
abductor – muscles that move a bone away from the
midline (deltoid, gluteus maximus)
adductor – muscles that move a bone closer to the
midline (gracilis, pectoralis major)
extensor – muscles that increase the angle of a joint
(tricep, quadriceps)
flexor – muscles that decrease the angle of a joint
(bicep, hamstrings)
sphincter – muscles that decrease the size of an
opening (esophogeal sphincter, rectal spincter)

36. Skeletal Muscle Action
isotonic contractions: when a muscle is actively shortening or lengthening ex. lifting weights
isometric contractions: when a muscle is not shortening or lengthening ex. pushing against an immovable object

37. Fatigue during muscular exercise:
b.v. in muscles dilate & blood flow and O2 delivery increases
muscle fatigue occurs after extended or strong muscle contractions and O2 & ATP can’t supply muscle fibers fast enough
oxygen debt – amount of O2 taken in to “pay back” resting metabolic conditions
if O2 is unavailable, glucose is converted into lactate which helps break down glucose for energy
production of lactic acid in the body causes soreness

38. 21. List 2 things that can happen when muscles are used irregularly.
Concept Check #6
21. List 2 things that can happen when muscles are used irregularly.
22. List 2 things that can happen when muscles are used regularly.
How do hypertrophy and hypotrophy (atrophy) differ?
24. Do all the muscle fibers (cells) in my arm contract when I pick up a pencil? Use the terms threshold stimulus and all or none theory in your explanation.

39. 26. What is the relationship between muscle fatigue and oxygen debt?
Concept Check #7
25. Explain the difference between isotonic and isometric contractions. Give an example of each.
26. What is the relationship between muscle fatigue and oxygen debt?

40. To keep swelling down apply cold 1st
Aging and Pathology of the Skeletal System
many disorders of the musculature are due to interactions with the skeletal and nervous systems
Strains vs. Sprains
strains – overworking the muscle’s force on joints and tendons
pain and swelling of fascia, joints, ligaments, and tendons
nerves signal pain when stretched or swollen (stiff)
sprains – more severe; sudden or violent stress
on a joint/muscle
tearing of a ligament, muscle, or tendon and
damage to nearby blood vessels
require time for tissue and protein replacement
To keep swelling down apply cold 1st
followed by continuous warmth to speed
healing

41. contusions – related to sprains; direct hit(s) to a muscle

42. Myopathy / Neuromuscular disorders
inability of the nervous system to communicate properly to muscles
1. mitochondrial myopathies – genetic abnormalities of the mitochondria; muscles can’t produce energy from food; muscles become easily cramped

43. 2. myosistis ossificans – caused by damage to soft muscle; bone growing within muscle tissue; pain during contraction
a. Nonhereditary b. Herditary (A.D.)
traumatica progressiva

44. 3. muscular dystrophy- involves progressive weakness in the voluntary muscles; inability of nervous system to stimulate muscle action; results in atrophy and wasting

45. Steroids on Muscles boost body’s ability to produce muscle
prevent muscle breakdown &
decreases recovery time
resemble chemical structure of
testosterone
{T} directs the body to produce
more or enhance male
characteristics (like increased
muscle mass, etc)

47. Aging of the Muscular System
natural causes  sarcopenia
cachexia  muscle loss usually associated with AIDS, cancer, starvation, anorexia, bulimia
decrease in neural stimulation -> atrophy
malnutrition / undernutrition  decrease in carbs and proteins  less energy and nutrients for repair and maintenance
decline in sex hormones and insulin-like growth factor –1 (IGF-1); needed for muscle cell growth, maintenance, & repair
physical therapies 
electrical stimulation pulses (causes muscles to retain protein)
muscle massages

48. 27. What are the differences between strains, sprains, and contusions?
Concept Check #8
27. What are the differences between strains, sprains, and contusions?
28. Name and describe 2 different types of myopathies.
29. What is cachexia in terms of muscle aging.
30. Describe 4 factors that contribute to muscle aging.

49. Case Study Investigation
Selected for an internship at National Space Biomedical Research Ins.
Required to monitor astronauts for NASA before, during, and after a space mission.
American astronaut spent 171 days in the space stations has to go through 3 weeks of physical therapy.
She lost 30% of her skeletal muscle even after following all the exercise programs NASA required. The average is less than 20%.
Questions:
Why did the American lose 30% of her skeletal muscle after her mission to space? Be specific.
2. She lost 10% more than the average astronaut. What else associated with her mission could have contributed to the American’s muscle loss?

50. CSI - ANSWER
much of the muscle’s actions go into counteracting the affects of gravity on the body; they have to work harder in gravity environments
regular resistance produces muscle mass and strength
weightlessness of space flight reduces the muscles need to work against gravity; muscles will lose their mass and strength and they atophy
protein metabolism  astronauts don’t receive large amounts of amino acids they need
sex hormones  decline in sex hormones from the stress of working in space for 6 mo